Three weeks of heat maintenance potentiates the benefits of heat acclimation in trained females

We investigated whether heat adaptation (HA) could be maintained in trained females following an initial acclimation period. The experimental group (EXP, n = 11) completed 10 sessions of HA over 2 weeks, followed by nine sessions of HA maintenance (HA_M) over 3 weeks. HA was induced with home-based stationary cycling while overdressing. A control group (CON, n = 4) was exposed to heart rate-matched thermoneutral training. Prior to and at the end of the acclimation period (PRE, MID) and following the maintenance period (POST), <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> <mml:annotation>$$ \dot{\mathrm{V}}{\mathrm{O}}_2\max $$</mml:annotation></mml:semantics> </mml:math> , peak power output (PPO), and hemoglobin mass (Hb_mass) were determined in 18°C, before a 20 km time trial (TT) in 35°C, 45% RH. During the TT, rectal and mean skin temperature (T_re, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>T</mml:mi> <mml:mo>¯</mml:mo></mml:mover> </mml:mrow> <mml:annotation>$$ \overline{\mathrm{T}} $$</mml:annotation></mml:semantics> </mml:math> _sk), heart rate, peak cardiac output ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mtext>peak</mml:mtext></mml:mrow> <mml:annotation>$$ \dot{Q}\mathrm{peak} $$</mml:annotation></mml:semantics> </mml:math> ), and sweat rate were measured. PPO increased (p = 0.0003) and TT times decreased (p < 0.0001) from PRE to MID and POST in EXP but not CON. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> <mml:annotation>$$ \dot{\mathrm{V}}{\mathrm{O}}_2\max $$</mml:annotation></mml:semantics> </mml:math> , T_re, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>T</mml:mi> <mml:mo>¯</mml:mo></mml:mover> </mml:mrow> <mml:annotation>$$ \overline{\mathrm{T}} $$</mml:annotation></mml:semantics> </mml:math> _sk, heart rate, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mtext>peak</mml:mtext></mml:mrow> <mml:annotation>$$ \dot{Q}\mathrm{peak} $$</mml:annotation></mml:semantics> </mml:math> remained stable in both groups. Sweat rate only increased in EXP from PRE to POST (p = 0.0197). Hb_mass did not change in EXP. HA_M potentiated hot exercise performance compared to HA, as demonstrated by improvements in both temperate and hot conditions. While HA_M suffices to further develop thermal resistance, it is unsuitable to increase Hb_mass following 10 days of HA or 3 weeks of HA_M. Our findings demonstrate that females can achieve HA by overdressing at home for 10 days and that HA_M provides further benefits.